Semiconductor light sources are well-known in the field of electro-optics for providing a means for generating light within a silicon chip. Examples of such semiconductor light sources include, e.g., semiconductor lasers, light emitting diodes (LED's), and electroluminescent (EL) display devices. Such semiconductor light sources; have been fabricated from sophisticated and expensive compound semiconductor technologies. However, those technologies are not directly compatible with or applicable to silicon very large scale integration (VLSI) chips.
Integrated optics chips often incorporate a semiconductor light source on the same chip as other integrated electronic circuitry, which yields a device capable of high-speed processing. However, many current optoelectronic and display systems use VLSI chips for performing signal processing; since the semiconductor light source fabricating technologies have heretofore not been sufficiently compatible with or applicable to VLSI chips, semiconductor light sources have by necessity been provided on separate chips which are electrically interfaced with the silicon VLSI circuit chips where a light source is called-for.
Silicon has an indirect optical band gap; the recombination of electrons and holes in bulk crystalline silicon produces very weak luminescence in the infrared, making silicon an unsuitable material for light sources for displays or optoelectronic applications. As a result, display technologies and optoelectronic technologies have developed based on semiconductor materials better suited as light sources. Semiconductor display devices are generally based on materials such as ZnS with heavy doping. Optoelectronic IC's are generally based on ternary and quaternary semiconductors compatible with GaAs or InP substrates, which rely on one of the epitaxial crystal growth techniques. The processing of these materials is radically different than the processing of standard silicon VLSI IC's, and is more expensive. The fast computational and signal processing power which has been developed for silicon VLSI circuits is not available in these more complex materials. Furthermore, these materials are not as stable as silicon in electronic circuits. Systems applications requiring fast computing and signal processing require interfacing these more complicated technologies with the silicon VLSI chips. This results in added expense, added weight, and added complexity.
Silicon VLSi chips have reached a level of complexity such that a primary limitation in the overall system speed and computing power of VLSI circuitry is the speed of information flow through the interconnects between chips. The prior art has provided electrical connections as interconnects between VLSI chips. These electrical connections are subject to inherent delays due to the distributed inductances and capacitances in the interconnects themselves. High-speed optical interfacing between VLSI chips has been impractical due to the lack of a technology which enables semiconductor light sources to be incorporated into VLSI chips; and, electrical interfaces cannot match the high speed and high capacity that is provided by direct optical interfacing between circuits. And, electrical interfacing is complex, bulky, heavy, and expensive. The large number of interconnects which are required for modern chips have presented a space problem. That is, throughput between VLSI chips has been limited by the number of interconnects which will fit on the VLSI chip. In addition, the electrical interconnections are vulnerable to electromagnetic pulse (EMP) and other forms of electromagnetic interference (EMI). The electrical interconnects also emit electromagnetic radiation, which is susceptible to interception and thus poses a security risk.
Previous light sources, such as light emitting diodes (LED's), have been fabricated from GaAs, GaP, and other multiple component semiconductor materials. LED's made from direct gap semiconductor material such as GaAs, operate simply as a result of carrier recombination in a P-N junction. LED's fabricated from indirect gap material, such as GaP, are implanted to produce excitonic complexes which assist the recombination in the P-N junction. Since silicon is an lndlrect band gap semiconductor, it does not luminesce to a usable extent as a result of carrier recombination in P-N junctions. Attempts to create excitonic complexes to assist the recombination in bulk silicon, as is common in GaP, have proved insufficient.
The prior art also includes LED devices made from porous silicon. However, porous silicon is highly unstable chemically and physically, and is fabricated using a complex electrochemical etched method.